Hearing aid and method for operating a hearing aid to suppress electromagnetic disturbance signals

ABSTRACT

Given a hearing aid comprising a microphone, a signal processing unit and an earphone, a detector element for detecting electromagnetic disturb signals is provided, as well as a filter element that is configured dependent on the recognized disturbance signals in order to suppress the disturbance signals. Furthermore, the hearing aid as a clock element for acquiring the clock frequency of the disturbance signal detected by the detector element, whereby the clock element serves the purpose of generating the system clock frequency of the hearing aid proceeding from the clock frequency of the disturbance signal. This enables a particularly efficient disturbance signal suppression.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a hearing aid having a microphone, asignal processing unit and an earphone, to a method for suppressingelectromagnetic disturb signals in a hearing aid of this type.

2. Description of the Prior Art

Signal processing in hearing aids can be impaired by electromagneticdisturb signals, for example by noise fields of mobile telephones. Animprovement of the electromagnetic compatibility (EMC) of hearing aids,for example by interconnect optimization and capacitive shielding ofmicrophones, cannot eliminate the noise sensitivity.

European Patent 0 843 427 discloses a system, which uses adaptive combfilters for suppressing periodic electromagnetic disturbance signals. Itis necessary to adapt the cutoff frequencies and bandwidths of the combfilter as accurately as possible to the disturbance signal, so that theuseful signal is impaired as little as possible.

SUMMARY OF THE INVENTION

An object of the invention is to provide a hearing aid and a method,wherein disturbance signals and noise fields are reliably suppressed.

The above object is achieved in accordance with the principles of thepresent invention in a method for suppressing electromagneticdisturbance signals in a hearing aid, and a hearing aid operatingaccording to the method, wherein a clock element acquires the clockfrequency of the disturbance signal that is detected by a detectorelement in the hearing aid, and the clock element generates a signal anda system clock frequency dependent on the clock frequency of thedisturbance signal.

The term “hearing aid” as used herein refers to separate hearing aidsthat can be worn at the head or at the body, to hearing aids that can beworn behind the ear, in the ear, to pocket hearing aids and also tohearing aids that can be implanted.

In the inventive hearing aid, it is initially determined via a detectorelement whether electromagnetic disturbance signals or noise fields arepresent. If this is the case, a filter element is configured dependingon the type of the recognized disturbance signals in order to suppressthe noise fields. In this way, the disturbance signals can be filteredout in a way that is adapted to the particular type of the noise fieldand therefore the filtering is particularly efficient. For example, acomb filter, whose filter characteristic is exactly adapted to therespective disturbance signal, is configured in the filter element. Thesystem clock of the hearing aid can be utilized for configuring the combfilter. Besides, the inventive hearing aid has a clock element foracquiring the clock frequency of the disturbance signal acquired by thedetector element. The acquired clock frequency of the disturbance signalis then used for generating the system clock frequency, particularly byfrequency multiplication. On the basis of the current clock frequency ofthe disturbance signal, the system clock frequency is newly generated.The clock frequency of the system clock element of the hearing aid,which is altered or falsified as a result of aging or drift, forexample, can be switched off and the newly generated system clockfrequency that is derived from the clock frequency of the disturb signalcan be used for operating and particularly for configuring the filterelement. As a result thereof, a particularly precisely configured filterelement is achieved, which is able to suppress the determineddisturbance signals in a particularly effective way.

If the clock element has a PLL circuit (“phase-locked-loop”), thegenerated system clock frequency can be generated as a rational multipleof the isolated and acquired disturb signal frequency.

A change element can be connected between the clock element and thesystem clock element, so that the previous system clock element, afterthe new system clock frequency has been generated, can be switched offand the hearing aid can be operated for generating a suitable filtercharacteristic with the newly derived system clock frequency.

In principle, the inventive hearing aid can be digitally or analogouslyconstructed. Given a digital construction, the hearing aid can have aDSP element (digital signal processor element) for a particularlyprecise signal processing having a number of versions. The filterelement for suppressing the disturb signals can be integrated into theDSP element or it can be arranged directly in front of the A-Dconverter, for example, for particularly effective suppression of thedisturbance signals at the end of the signal transmission chain.

After the disturbance signals have been detected, a filter element isinventively configured dependent on the detected disturbance signals forthe adapted suppression of the disturbance signals.

The suppression of the disturbance signals is particularly efficientwhen the clock frequency of the disturbance signal is initially acquiredand isolated and when the system clock frequency is subsequentlygenerated particularly by frequency multiplication. As a result of thisgenerated system clock frequency, the filter element can be particularlyprecisely configured (e.g. high-pass filter, low-pass filter, combfilter, FFT), since the system clock of the hearing aid, that is may befalsified as a result of aging or drift, is not used.

In this version of the inventive method, the disturbance signal itselfgenerates a suitable filtering for suppressing the disturbance signal.

The inventive method is particularly suited for of suppressingelectromagnetic disturbance signals of mobile telephones (e.g. accordingto the GSM standard or DECT standard) and for acquiring the interferencecharacteristics of known mobile radio networks (e.g. D1 network, D2network, E network, E-plus network).

Electromagnetic noise fields which occur in connection with the networkfrequency can be detected and suppressed when the hearing aid isoperated by means of a telephone coil.

In addition, the detector element can be used for detecting, forexample, the ringing or the activation of the mobile telephone due tothe arising frequency signals and for making it perceptible directly inthe hearing aid.

DESCRIPTION OF THE DRAWING

The single FIGURE is a schematic block diagram of a hearing aidconstructed and operating in accordance with the principles of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The basic diagram shows a hearing aid having a microphone 1, a signalprocessing unit 8 and an earphone 7. The A-D converter 5, thepreamplifier 2, the DSP element 3, the postamplifier 4 and the D-Aconverter 6 are arranged in the signal processing path between themicrophone 1 and the earphone 7.

The hearing aid receives the electromagnetic disturbance signal 14 viathe detector element 12 and therefore detects the presence of, forexample, a GSM telephone in the D1 network. The detector element 12transmits the information about the detected noise field type (namelyGSM telephone, D1 network) to the DSP element 3, so that the filterelement 13 can be configured in a way that is adapted to the detectednoise field type for the particularly effective noise field suppression.

As shown, the filter element can be integrated into the DSP element 3or, for a particularly efficient noise field suppression, can bearranged at the end of the signal transmission chain between themicrophone 1 and the earphone 7—particularly after the postamplifier 4and in front of the D-A converter 6 (not shown).

In the exemplary embodiment of the hearing aid, the detector element 12forwards the information via the detected noise field type to the clockelement 11, which may be a PLL circuit, in particular. The clockfrequency is acquired and isolated in the clock element 11 and thesystem clock that is normally provided by the system clock element 10 isnewly generated by frequency multiplication. For example, when the noisefield has a clock frequency of 200 Hz, which has been isolated, a systemclock frequency of 20 kHz can be generated by frequency multiplicationwith the factor 100, whereby the system clock frequency serves thepurpose of directly timing the DSP element 3 in that the changeoverswitch 9 is operated when the system clock element 10 is switched off.In this way, a particularly efficient noise field suppression can occurin the filter element 13 as a result of the newly generated system clockof the clock element 11.

The clock of the system clock element 10, that may be falsified as aresult of aging or a temperature drift, is switched off, so that afaulty configuration of the filter element 13 by a falsified systemclock is prevented.

The clock element 11 receives necessary bits of information from the DSPelement 3 for generating the system clock, for example. As a result ofthe frequency multiplication, the system clock can be either generatedexactly or with a slight deviation.

The stored coefficient sets can be updated and can include all datavariables or correcting variables, which are necessary for an effectiveinterference elimination by the filter element 13.

Although modifications and changes may be suggested by those skilled inthe art, it is the intention of the inventors to embody within thepatent warranted hereon all changes and modifications as reasonably andproperly come within the scope of their contribution to the art.

I claim:
 1. A hearing aid comprising: a microphone which converts anincoming audio signal into an electrical microphone output signal; asignal processing unit connected to said microphone for processing saidmicrophone output signal to produce a processed signal, said signalprocessing unit including a filter element which is configurabledependent on a system clock frequency in said signal processing unit; adetector element for detecting externally-originating electromagneticdisturbance signals, said disturbance signals having a clock frequency;a clock element in said signal processing unit, connected to saiddetector element, for identifying the clock frequency of the disturbancesignal and wherein said signal processing unit generates said systemclock frequency dependent on said clock frequency of said disturbancesignal to configure said filter element to filter said disturbancesignal out of said processed signal; and an earphone supplied with saidprocessed signal for converting said processed signal into an audiooutput signal.
 2. A hearing aid as claimed in claim 1 wherein said clockelement is a phase-locked loop circuit.
 3. A hearing aid as claimed inclaim 1 wherein said signal processing unit includes a system clockwhich generates said system clock frequency, and further comprising aprocessor in said signal processing unit connected to said filter, whichconfigures said filter, a system clock generator which generates saidsystem clock frequency, and a changeover switch connected to said clockelement, said system clock generator and said processor for selectivelysupplying one of said system clock frequency and said clock frequency ofsaid disturbance signal to said processor.
 4. A hearing aid as claimedin claim 3 wherein said processor is a digital signal processor.
 5. Ahearing aid as claimed in claim 4 wherein said filter element isintegrated into said digital signal processor.
 6. A method for operatinga hearing aid having a microphone which converts incoming audio signalsinto electrical microphone output signals, a signal processing unitwhich processes said microphone output signals to produce a processedsignal, and an earphone supplied with said processed signal forconverting said processed signal into an audio output signal, saidmethod comprising the steps of: in said hearing aid, detectingexternally-originating electromagnetic disturbance signals, saiddisturbance signals having a clock frequency; in said signal processingunit, identifying the clock frequency of the disturbance signal;generating a system clock frequency for use in producing said processedsignal dependent on said clock frequency of said disturbance signal; andconfiguring a filter element in said signal processing unit using saidsystem clock frequency, dependent on said clock frequency of saiddisturbance signal, to filter said disturbance signal out of saidprocessed signal.
 7. A method as claimed in claim 6 wherein the step ofdetecting externally-originating electromagnetic disturbance signalscomprises detecting a disturbance signal originating from a mobiletelephone.
 8. A method as claimed in claim 6 wherein the step ofdetecting externally-originating electromagnetic disturbance signalcomprises detecting a noise field associated with a mobile telephone. 9.A method as claimed in claim 6 wherein the step of detecting anexternally-originating electromagnetic disturbance signal comprisesdetecting a disturbance signal originating from a mobile telephone, andwherein said method comprises the additional steps of employing atelephone coil in place of said microphone for picking up incomingtelephone audio signals and converting said incoming telephone audiosignals into a coil output signal supplied to said signal processingunit for producing said processed signal, and detecting said disturbancesignals when said telephone coil is used in place of said microphone.10. A method as claimed in claim 6 comprising employing a comb filter assaid filter element.
 11. A method as claimed in claim 6 wherein saidcomb filter is configurable according to a selected one of a pluralityof coefficient sets, and comprising the steps of storing saidcoefficient sets in said signal processing unit and selecting one ofsaid coefficient sets for configuring said comb filter dependent on saidclock frequency of said disturbance signal.